(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of forming a silicon-on-insulator (SOI) device having a buried layer in the fabrication of integrated circuits.
(2) Description of the Prior Art
As 3C (computer, communication, and consumer) integration becomes a worldwide trend, Bipolar Junction Transistor (BJT) devices are coming into high demand. Because of their good device isolation properties and resulting superb device performance characteristics, silicon-on-insulator (SOI) wafers are becoming more and more popular. Silicon-on-insulator technology is discussed in Silicon Processing for the VLSI Eraxe2x80x94Volume II,_by Stanley Wolf, Lattice Press, Sunset Beach, Calif., c. 1990, on pages 66-78. Two of the many methods of making SOI wafers will be described with reference to FIGS. 1A, 1B, 2A, 2B, and 2C.
Referring now more particularly to FIG. 1A, there is shown a semiconductor substrate 1, preferably composed of monocrystalline silicon. A layer of silicon oxide 2 is formed on the surface of the substrate. A second monocrystalline substrate 3 has a silicon oxide layer 4 formed thereon. The first substrate 1 is turned upside down and the two substrates are joined together at the surface of their oxide layers by pressurizing and strengthening during later annealing. The substrate 1 is etched back or polished to reduce its thickness, as shown in FIG. 1B. This method can be referred to as the bonded and etched back SOI (BESOI).
A second method is known as the Unibond(trademark) method. The SMART-CUT Unibond(trademark) method is discussed in the three papers, xe2x80x9cSilicon on Insulator Material Technology,xe2x80x9d by M. Bruel, Electronics Letters, Vol. 31, No. 14, Jul. 6, 1995, pp. 1201-1202, xe2x80x9cxe2x80x9cSMART CUTxe2x80x99: A Promising New SOI Material Technology,xe2x80x9d by M. Bruel et al, Proceedings 1995 IEEE International SOI Conference, October 1995, pp. 178-179, and xe2x80x9cCleaning and Polishing as Key Steps for SMART-CUT SOI Process,xe2x80x9d by H. Moriceau et al, Proceedings 1996 IEEE International SOI Conference, October 1996, pp. 152-153. Referring now to FIG. 2A, there is shown a monocrystalline silicon semiconductor substrate 1. An oxide layer 2 is grown on the surface of the substrate 1. Hydrogen ions are implanted into the wafer to a level 5 where splitting is designed to take place. Referring to FIG. 2B, a second monocrystalline substrate 3 has a silicon oxide layer 4 formed thereon. The first substrate 1 is turned upside down and the two substrates are joined together at the surface of their oxide layers by pressurizing and strengthening during later annealing. During a heat treatment at 400-600xc2x0 C., the wafer 1 will split at the level of the hydrogen ion penetration 5, leaving behind a thin layer of silicon 6, as shown in FIG. 2C. The substrate 1 that has been split off is re-usable.
In order to make BJT and BICMOS integrated circuit devices of high performance using SOI wafers, it is necessary to make SOI wafers having a buried layer structure within. U.S. Pat. No. 5,488,012 to McCarthy teaches a method of growing a sequence of single or multiple etch stop layers ending with a thin silicon layer on a silicon substrate. The silicon layer is bonded to a glass substrate and the silicon substrate is removed. U.S. Pat. No. 5,286,670 to Kang et al shows a method of forming a semiconductor device having electrical elements buried within a SOI substrate. A layer of polysilicon covers the buried electrical elements and is polished before being bonded to a semiconductor substrate. U.S. Pat. No. 5,360,752 to Brady et al teaches a method of radiation hardening the buried oxide in a SOI structure by implanting ions into the oxide layer.
A principal object of the present invention is to provide an effective and very manufacturable method of forming a silicon-on-insulator device having a buried layer in the fabrication of an integrated circuit.
Another object of the present invention is to provide a method of forming a silicon-on-insulator device having a buried layer formed by ion implantation in the fabrication of an integrated circuit.
Yet another object of the present invention is to provide a method of forming a silicon-on-insulator device having a buried layer formed by silicide in the fabrication of an integrated circuit.
A further object of the invention is to provide a method of forming a bonded and etched back silicon-on-insulator device (BESOI) having a buried layer in the fabrication of an integrated circuit.
A still further object of the invention is to provide a method of forming a Unibond(trademark) silicon-on-insulator device having a buried layer in the fabrication of an integrated circuit.
In accordance with the objects of this invention the method of forming a silicon-on-insulator device having a buried layer is achieved. Ions are implanted into a first semiconductor substrate where it is not covered by a photoresist mask to form implanted regions. Alternatively, a silicide layer over the first semiconductor substrate is patterned to leave silicide regions. A first oxide layer is formed overlying the first semiconductor substrate whereby the implanted regions or the silicide regions form the buried layer structure. A second oxide layer is formed overlying a second semiconductor substrate. The first and second oxide layers are bonded together to form the wafer, using either the bond and etch back or the Unibond(trademark) method to complete formation of an silicon-on-insulator wafer having a buried layer structure in the fabrication of an integrated circuit.